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	<h1 id="firstHeading" class="firstHeading" lang="en">Control points</h1>
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		<div id="siteSub" class="noprint">From PanoTools.org Wiki</div>
		
		
		
		
		
		
		<div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr"><div class="mw-parser-output"><p><br />
Most techniques for aligning photographs involve <b>Control points</b> at some stage.
</p><p>The principle is that by identifying the same physical features (a door, a tree, whatever) in
more than one photo, it is possible to establish facts about the relative camera orientations
mathematically.  The <a href="Pano12.html" title="Pano12">pano12</a> library contains a program called <a href="PTOptimizer.html" title="PTOptimizer">PTOptimizer</a> that does this job.
</p><p>Each of these real-world features is defined as a <i>pair</i> of control points.  Usually two
<i>pairs</i> of control points are sufficient to simply align one photograph against another, and
more photographs require more <i>pairs</i> - This alignment process is called <i>control point optimisation</i>.
</p><p>As well as adjusting this <a href="Roll.html" title="Roll">roll</a>, <a href="Pitch.html" title="Pitch">pitch</a> &amp; <a href="Yaw.html" title="Yaw">yaw</a> orientation, often
<a href="Field_of_View.html" title="Field of View">Field of View</a> and other aspects of the <a href="Lens_correction_model.html" title="Lens correction model">lens correction model</a> are <i>optimised</i> at the same
time.
</p><p>Control points can be picked manually by clicking with a mouse, and there are a number of
GUI front-ends<a class="external" href="https://wiki.panotools.org/GUI_front-ends">[*]</a> to help you do this.  There are other tools such as <a href="Autopano-sift.html" title="Autopano-sift">autopano-sift</a> and
<a href="Autopano.html" title="Autopano">autopano</a> that can generate control points automatically with some limitations.
</p><p>In addition to these simple control points, <a href="PTOptimizer.html" title="PTOptimizer">PTOptimizer</a> allows users to define
<a href="Horizontal_control_points.html" title="Horizontal control points">horizontal control points</a>, <a href="Vertical_control_points.html" title="Vertical control points">vertical control points</a> and <a href="Straight_line_control_points.html" title="Straight line control points">straight line control points</a>.
These have various uses, but mainly they are good for Leveling a Finished Panorama<a class="external" href="https://wiki.panotools.org/Leveling_a_Finished_Panorama">[*]</a> and
<a href="Perspective_correction.html" title="Perspective correction">perspective correction</a>.
</p>
<h2><a name="Historical_note"><span class="mw-headline">Historical note</span></a></h2>
<p>Before PTPicker<a class="external" href="https://wiki.panotools.org/PTPicker">[*]</a>, the GUI front-ends<a class="external" href="https://wiki.panotools.org/GUI_front-ends">[*]</a> and <a href="Autopano.html" title="Autopano">autopano</a>/<a href="Autopano-sift.html" title="Autopano-sift">autopano-sift</a>, control points
were set by cutting and pasting the flags below into source photos.  You were allowed up to
twenty pairs of points and twenty images - Panorama Tools would read the bar codes embedded in
the flags and generate a script for <a href="PTOptimizer.html" title="PTOptimizer">PTOptimizer</a>.
</p><p>This functionality is still available in the <i>adjust</i> menu of the Panorama GIMP plug-in<a class="external" href="https://wiki.panotools.org/Panorama_GIMP_plug-in">[*]</a>,
however the technique is extremely laborious and <b>definitely not recommended</b>.
</p><p><img alt="Barcode flags used by the original panorama tools control point picking technique" src="Flags.png" decoding="async" width="272" height="526" />
</p>

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